Chimeric Yellow Fever/Dengue Virus as a Candidate Dengue Vaccine: Quantitation of the Dengue Virus-Specific CD8 T-Cell Response

We have constructed a chimeric yellow fever/dengue (YF/DEN) virus, which expresses the premembrane (prM) and envelope (E) genes from DEN type 2 (DEN-2) virus in a YF virus (YFV-17D) genetic background. Immunization of BALB/c mice with this chimeric virus induced a CD8 T-cell response specific for the DEN-2 virus prM and E proteins. This response protected YF/DEN virus-immunized mice against lethal dengue encephalitis. Control mice immunized with the parental YFV-17D were not protected against DEN-2 virus challenge, indicating that protection was mediated by the DEN-2 virus prM- and E-specific immune responses. YF/DEN vaccine-primed CD8 T cells expanded and were efficiently recruited into the central nervous systems of DEN-2 virus challenged mice. At 5 days after challenge, 3 to 4% of CD8 T cells in the spleen were specific for the prM and E proteins, and 34% of CD8 T cells in the central nervous system recognized these proteins. Depletion of either CD4 or CD8 T cells, or both, strongly reduced the protective efficacy of the YF/DEN virus, stressing the key role of the antiviral T-cell response

Cyclophosphamide Chemotherapy Sensitizes Tumor Cells to TRAIL-Dependent CD8 T Cell-Mediated Immune Attack Resulting in Suppression of Tumor Growth

Background: Anti-cancer chemotherapy can be simultaneously lymphodepleting and immunostimulatory. Pre-clinical models clearly demonstrate that chemotherapy can synergize with immunotherapy, raising the question how the immune system can be mobilized to generate anti-tumor immune responses in the context of chemotherapy. Methods and Findings: We used a mouse model of malignant mesothelioma, AB1-HA, to investigate T cell-dependent tumor resolution after chemotherapy. Established AB1-HA tumors were cured by a single dose of cyclophosphamide in a CD8 T cell- and NK cell-dependent manner. This treatment was associated with an IFN-α/β response and a profound negative impact on the anti-tumor and total CD8 T cell responses. Despite this negative effect, CD8 T cells were essential for curative responses. The important effector molecules used by the anti-tumor immune response included IFN-γ and TRAIL. The importance of TRAIL was supported by experiments in nude mice where the lack of functional T cells could be compensated by agonistic anti-TRAIL-receptor (DR5) antibodies. Conclusion: The data support a model in which chemotherapy sensitizes tumor cells for T cell-, and possibly NK cell-, mediated apoptosis. A key role of tumor cell sensitization to immune attack is supported by the role of TRAIL in tumor resolution and explains the paradox of successful CD8 T cell-dependent anti-tumor responses in the absence of CD8 T cell expansion

H5N1 Influenza Vaccine Formulated with AS03A Induces Strong Cross-Reactive and Polyfunctional CD4 T-Cell Responses

Objective Adjuvantation of an H5N1 split-virion influenza vaccine with AS03(A) substantially reduces the antigen dose required to produce a putatively protective humoral response and promotes cross-clade neutralizing responses. We determined the effect of adjuvantation on antibody persistence and B- and T-cell-mediated immune responses. Methods Two vaccinations with a split-virion A/Vietnam/1194/2004 (H5N1, clade 1) vaccine containing 3.75-30 mu g hemagglutinin and formulated with or without adjuvant were administered to groups of 50 volunteers aged 18-60 years. Results Adjuvantation of the vaccine led to better persistence of neutralizing and hemagglutination-inhibiting antibodies and higher frequencies of antigen-specific memory B cells. Cross-reactive and polyfunctional H5N1-specific CD4 T cells were detected at baseline and were amplified by vaccination. Expansion of CD4 T cells was enhanced by adjuvantation. Conclusion Formulation of the H5N1 vaccine with AS03(A) enhances antibody persistence and induces stronger T- and B-cell responses. The cross-clade T-cell immunity indicates that the adjuvanted vaccine primes individuals to respond to either infection and/or subsequent vaccination with strains drifted from the primary vaccine strain

Innate immunity defines the capacity of antiviral T cells to limit persistent infection

Effective immunity requires the coordinated activation of innate and adaptive immune responses. Natural killer (NK) cells are central innate immune effectors, but can also affect the generation of acquired immune responses to viruses and malignancies. How NK cells influence the efficacy of adaptive immunity, however, is poorly understood. Here, we show that NK cells negatively regulate the duration and effectiveness of virus-specific CD4+ and CD8+ T cell responses by limiting exposure of T cells to infected antigen-presenting cells. This impacts the quality of T cell responses and the ability to limit viral persistence. Our studies provide unexpected insights into novel interplays between innate and adaptive immune effectors, and define the critical requirements for efficient control of viral persistence

Elicitation of broadly protective sarbecovirus immunity by receptor-binding domain nanoparticle vaccines

Understanding vaccine-elicited protection against SARS-CoV-2 variants and other sarbecoviruses is key for guiding public health policies. We show that a clinical stage multivalent SARS-CoV-2 spike receptor-binding domain nanoparticle vaccine (RBD-NP) protects mice from SARS-CoV-2 challenge after a single immunization, indicating a potential dose-sparing strategy. We benchmarked serum neutralizing activity elicited by RBD-NP in non-human primates against a lead prefusion-stabilized SARS-CoV-2 spike (HexaPro) using a panel of circulating mutants. Polyclonal antibodies elicited by both vaccines are similarly resilient to many RBD residue substitutions tested although mutations at and surrounding position 484 have negative consequences for neutralization. Mosaic and cocktail nanoparticle immunogens displaying multiple sarbecovirus RBDs elicit broad neutralizing activity in mice and protect mice against SARS-CoV challenge even in the absence of SARS-CoV RBD in the vaccine. This study provides proof of principle that multivalent sarbecovirus RBD-NPs induce heterotypic protection and motivates advancing such broadly protective sarbecovirus vaccines to the clinic

Characterization of T-cell immune responses in clinical trials of the candidate RTS,S malaria vaccine

The candidate malaria vaccine RTS,S has demonstrated 45.7% efficacy over 18 months against all clinical disease in a phase-III field study of African children. RTS,S targets the circumsporozoite protein (CSP), which is expressed on the Plasmodium sporozoite during the pre-erythrocyte stage of its life-cycle; the stage between mosquito bite and liver infection. Early in the development of RTS,S, it was recognized that CSP-specific cell-mediated immunity (CMI) was required to complement CSP-specific antibody-mediated immunity. In reviewing RTS,S clinical studies, associations between protection and various types of CMI (CSP-specific CD4+ T cells and INF-γ ELISPOTs) have been identified, but not consistently. It is plausible that certain CD4+ T cells support antibody responses or co-operate with other immune-cell types to potentially elicit protection. However, the identities of vaccine correlates of protection, implicating either CSP-specific antibodies or T cells remain elusive, suggesting that RTS,S clinical trials may benefit from additional immunogenicity analyses that can be informed by the results of controlled human malaria infection studies

Mutagenesis of the RGD Motif in the Yellow Fever Virus 17D Envelope Protein

The envelope protein of yellow fever virus 17D (YFV-17D) contains a solvent-exposed RGD motif, which has led to the suggestion that integrins may function as cellular receptors for YFV-17D. We found that mutating the RGD motif to RGE had no effect on viral titers, whereas changing RGD to TGD, TGE, TAD, TAE, or RGS led to reduced titers. Substitution of RGD by RAD or RAE yielded RNA genomes that replicated in mammalian cells but could not spread to neighboring cells at 37°C. These mutants did spread through the cell monolayer at 30°C (both in mosquito cells and in SW13 cells) and viruses grown at this temperature were capable of infecting mammalian cells at 37°C. These results strongly suggest that RGD-mediated integrin binding does not play a major role in YFV-17D entry, since the RGD to RAD mutation, as well as many or all of the other mutations studied, should disrupt all RGD-dependent integrin binding. However, the RGD to RAD or RAE mutations (as well as TAD and TAE) severely destabilized the envelope protein at 37°C, providing an explanation for the observed phenotype. Implications of these findings are discussed in light of the fact that mutations that alter tropism or virulence in different flaviviruses are often found within the loop containing the RGD motif

Recombinant Vaccinia Virus-Induced T-Cell Immunity: Quantitation of the Response to the Virus Vector and the Foreign Epitope

Recombinant vaccinia viruses (rVV) have been extensively used as vaccines, but there is little information about the total magnitude of the VV-specific T-cell response and how this compares to the immune response to the foreign gene(s) expressed by the rVV. To address this issue, we quantitated the T-cell responses to both the viral vector and the insert following the infection of mice with VV expressing a cytotoxic T lymphocyte (CTL) epitope (NP118-126) from lymphocytic choriomeningitis virus (LCMV). The LCMV epitope-specific response was quantitated by intracellular cytokine staining after stimulation with the specific peptide. To analyze the total VV-specific response, we developed a simple intracellular cytokine staining assay using VV-infected major histocompatibility complex class I and II matched cells as stimulators. Using this approach, we made the following determinations. (i) VV-NP118 induced potent and long-lasting CD8 and CD4 T-cell responses to the vector; at the peak of the response (∼1 week), there were ∼10(7) VV-specific CD8 T cells (25% of the CD8 T cells) and ∼10(6) VV-specific CD4 T cells (∼5% of the CD4 T cells) in the spleen. These numbers decreased to ∼5 × 10(5) CD8 T cells (∼5% frequency) and ∼10(5) CD4 T cells (∼0.5% frequency), respectively, by day 30 and were then stably maintained at these levels for >300 days. The size of this VV-specific T-cell response was comparable to that of the T-cell response induced following an acute LCMV infection. (ii) VV-specific CD8 and CD4 T cells were capable of producing gamma interferon (IFN-γ), tumor necrosis factor alpha (TNF-α), and interleukin-2; all cells were able to make IFN-γ, a subset produced both IFN-γ and TNF-α, and another subset produced all three cytokines. (iii) The CD8 T-cell response to the foreign gene (LCMV NP118-126 epitope) was coordinately regulated with the response to the vector during all three phases (expansion, contraction, and memory) of the T-cell response. The total number of CD8 T cells responding to NP118-126 were ∼20- to 30-fold lower than the number responding to the VV vector (∼1% at the peak and 0.2% in memory). This study provides a better understanding of T-cell immunity induced by VV-based vaccines, and in addition, the technique described in the study can be readily extended to other viral vectors to determine the ratio of the T-cell response to the insert versus the vector. This information will be useful in optimizing prime-boost regimens for vaccination

Post-hoc analysis from phase III trials of human papillomavirus vaccines: considerations on impact on non-vaccine types

Background: Substantial heterogeneity has been reported in efficacy against high-grade cervical intraepithelial neoplasia (CIN) irrespective of HPV type in phase III results for bivalent and quadrivalent human papillomavirus virus (HPV) vaccines (AS04-HPV and qHPV). Real-world data recently confirmed a very high overall impact of AS04-HPV, supporting the validity of the observed heterogeneity. To explore the reasons for heterogeneous efficacy, we assessed vaccine impact on high-grade lesions not caused by vaccine types. Research methods: We extracted case counts of CIN lesions containing (1) at least one vaccine HPV type, (2) at least one vaccine HPV type and a high-risk non-vaccine type (co-infections) and (3) no vaccine types (non-vaccine or no high-risk HPV types). Based on these, Phase III cross-protective efficacies were estimated with exclusion (3) and with inclusion (2 and 3) of co-infections. Results: Cross-protective efficacy of AS04-HPV against CIN3 lesions ranges from 81.3% (95%CI: 34.7;96.5) (excluding co-infections) to 88.5% (95%CI:62.4;97.8) (including co-infections). For qHPV the efficacy ranges from −58.7% (95%CI: −180.5;8.5) (excluding co-infections) to 13.1% (95%CI: −39.0;45.9) (including co-infections). Conclusions: Heterogenous overall efficacy against CIN3 between AS04-HPV and qHPV is driven by differential efficacy against lesions that do not contain vaccine types, which may be related to the impact of different adjuvants on the immune response